This invention relates to a method of controlling the operating amount of an operation control means for an internal combustion engine, and more particularly to a method of this kind which is adapted to correct a desired or target value of the operating amount of such operation control means in a simple and inexpensive manner responsive to the temperature of intake air being supplied to the engine for improvement of the driveability of the engine over all operating regions of the engine inclusive of low load operating regions such as an idling region.
A method has been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos. 58-88436 and 53-8434, which determines a basic operating amount of operation control means for controlling the operation of the engine, such as a basic fuel injection amount to be supplied to the engine by a fuel supply quantity control system, a basic value of spark ignition timing to be controlled by an ignition timing control system, and a basic recirculation amount of exhaust gases to be controlled by an exhaust gas recirculation control system, in dependence on values of engine operating parameters indicative of loaded conditions of the engine, such as absolute pressure in the intake pipe of the engine and engine rotational speed, and corrects the basic operating amount thus determined in response to the temperature of intake air being supplied to the engine, to thereby set a desired operating amount for the operation control means with accuracy.
However, while the engine is operating in a low load condition such as at idle, the intake pipe absolute pressure has a reduced rate of change relative to the lapse of time with respect to a rate of change in the engine rotational speed relative to the lapse of time. Therefore, according to the above proposed method of determining operating amounts of the operation control means in dependence on the intake pipe absolute pressure and the engine rotational speed (generally called "the speed density method", and hereinafter merely referred to as "the SD method"), it is difficult to set with accuracy an operating amount such as a fuel supply quantity in accordance with the state of condition of the engine, thus causing hunting of the engine rotation, during operation of the engine in such a low load condition. In view of the foregoing, a method (hereinafter merely called "the KMe method") has been proposed, e.g. by Japanese Patent Publication No. 52-6414, which is based upon the recognition that the quantity of intake air passing the throttle valve is not dependent upon either of pressure PBA in the intake pipe downstream of the throttle valve and pressure of the exhaust gases while the engine is operating in a particular low load condition wherein the ratio PBA/PA' of intake pipe pressure PBA downstream of the throttle valve to intake pipe pressure PA' upstream of the throttle valve is below a critical pressure ratio (=0.528) at which the intake air forms a sonic flow, and accordingly the quantity of intake air can be determined solely in dependence on the valve opening of the throttle valve, if the intake pipe pressure PA' upstream of the throttle valve remains constant. Therefore, this proposed method detects the valve opening of the throttle valve alone to thereby detect the quantity of intake air with accuracy while the engine is operating in the above-mentioned particular low load condition, and then sets an operating amount such as a fuel injection quantity on the basis of the detected value of the intake air quantity.
Also a value of an operating amount determined by the above KMe method requires correction responsive to a change in the intake air temperature in a manner proper to the KMe method different from a manner of correction applied to the SD method. That is, while according to the SD method the detection of the intake air temperature should desirably be made at a location as close to the intake valve as possible, such detection according to the KMe method has to be made at a location immediately upstream of the throttle valve, because the flow rate of intake air in gravity or weight intrinsically varies in response to a change in the temperature of intake air immediately upstream of the throttle valve. However, if both the SD method and the KMe method are employed for correcting an operating amount in response to the intake air temperature in a selective manner dependent upon loaded conditions of the engine, to provide two separate intake air temperature sensors for respective exclusive use for these methods will render the control system complicate in structure and result in an increased manufacturing cost.